1. Field of the Invention
The present invention relates to a wireless communication system and a receiving device that utilize MIMO (Multiple Input Multiple Output)-OFDM (Orthogonal Frequency Division Multiplexing).
2. Description of the Related Art
A MIMO (Multi Input and Multi Output) communication system exists as a communication system capable of increasing transmission rates (capacity of transmission) by transmitting the same or different data simultaneously from a plurality of antennas by use of the same frequency band. The MIMO communication system is that transmission data are split into Ns-pieces of different data streams, and the respective transmission data streams are simultaneously transmitted from a plurality (Nt-pieces) of transmitting antennas, and these transmitted signals are multiplexed through a variety of communication paths and thus received by a plurality (Nr-pieces) of receiving antennas.
The MIMO receiving device separates, based on the signals received from the receiving antennas, for example, the MIMO channels into Ns-pieces of independent channels, thereby estimating a channel status. Information on this estimated channel status (which will hereinafter be referred to as channel status information (CSI)) is sent to the MIMO transmitting device, wherein the MIMO transmitting device utilizes the CSI for adaptive modulation, adaptive transmission power control, precoding and so on.
There is a MIMO-OFDM wireless communication system as a next generation wireless communication system in which OFDM (Orthogonal Frequency Division Multiplexing) defined as a multi-carrier transmission method is applied to this MIMO transmission method. FIG. 17 is a diagram showing an example of a device configuration of a MIMO-OFDM wireless communication transmitting device that uses a conventional linear precoder. The transmitting device shown in FIG. 17 includes an error correction coding unit (which will hereinafter be referred to as an FEC (Forward Error Correction) encoder) 10, a puncturing unit 11, a serial/parallel converting unit (which will hereinafter be abbreviated to an S/P converting unit) 12, frequency interleavers 13-1 through 13-Ns, constellation mappers 14-1 through 14-Ns, a preceding unit 15, inverse fast Fourier transform (which will hereinafter be abbreviated to IFFT) units 16-1 through 16-Nt, guard interval insertion units 17-1 through 17-Nt, transmitting antennas 18-1 through 18-Nt, and so on.
In the transmitting device, the transmission data are encoded based on a predetermined error correction code (the FEC encoder 10), then compressed (puncturing unit 11) and split into Ns-pieces of data streams by the S/P converting unit 12. The data streams are allocated to subcarrier signals having predetermined frequencies by the frequency interleavers 13-1 through 13-Ns, and the respective constellation mappers 14-1 through 14-Ns modulate the subcarriers signals by a predetermined modulation method on the basis of the data streams allocated to these subcarrier signals.
The modulated subcarrier signals are mapped to the transmitting antennas 18-1 through 18-Nt on the basis of the CSI by the preceding unit 15. Thus, the respective signals mapped to the transmitting antennas are inverse-fast-Fourier-transformed by the IFFT units 16-1 through 16-Nt, then GI insertion units 17-1 through 17-Nt insert the guard intervals in the signals, and these GI-inserted signals are transmitted from the transmitting antennas 18-1 through 18-Nt. Note that the CSI is generated through the channel estimation of the receiving device, and the transmitting device is notified of this generated CSI.
In the MIMO-OFDM wireless communication system using this type of conventional linear precoder, the number of transmission data streams (Ns) is generally required to be less than the number of transmitting antennas (Nt) in order to improve error rate performance. Further, in the transmitting device, it is required for attaining this purpose that the constellation mappers 14-1 through 14-Ns adaptively select the modulation method on the basis of the CSI etc, and that other function units conduct adaptive transmission power control.
Note that the conventional arts related to the present invention of the application are disclosed in the following documents. The conventional art documents are “Japanese Unexamined Patent Application Publication No. 2004-534456”, “Japanese Unexamined Patent Application Publication No. 2003-530010”, “Japanese Patent Application Laid-Open Publication No. 2004-304760”, and “Japanese Patent Application Laid-Open Publication No. 2004-254285.”
In the conventional MIMO-OFDM wireless communication system described above, however, if the number of transmitting/receiving antennas increases while actualizing the adaptive modulation and the adaptive transmission power control, circuit configurations of the transmitting device and the receiving device become complicated, a circuit scale expands, and there arise problems such as cost-up and an increase in power consumption.